Bone is not inert material. It is living tissue in constant remodelling, with osteoclasts continuously breaking down old bone and osteoblasts building new bone. In healthy adults, this process maintains roughly equal rates of resorption and formation. Oestrogen suppresses osteoclast activity, keeping resorption in check. When oestrogen falls at menopause, the brake on osteoclast activity is released. Bone resorption accelerates dramatically while bone formation remains unchanged, producing net bone loss at a rate of 2 to 5 percent per year in the first years after menopause.
The Scale of the Problem
Riggs et al., publishing in the Journal of Bone and Mineral Research, documented that women lose approximately 20 percent of their total bone mineral density in the 5 to 7 years immediately following menopause. By age 65, a typical woman has lost roughly 30 to 35 percent of her peak bone mass. The clinical consequence is that one in two women over 50 will experience a fracture related to osteoporosis, compared to one in five men. Hip fracture carries a one-year mortality rate of approximately 20 percent in older adults.
The DEXA Scan
Bone density is measured by dual-energy X-ray absorptiometry. Results are reported as T-scores: the standard deviation difference between the patient's bone density and the mean for healthy young adults. A T-score between -1.0 and -2.5 indicates osteopenia, where bone density is below normal but not yet in the fracture-risk range. Below -2.5 is defined as osteoporosis. Many women are not tested until they have their first fracture, by which point substantial bone has already been lost.
What the Evidence Supports for Protection
- HRT started at menopause: the most effective intervention for preventing post-menopausal bone loss; reduces fracture risk by 30 to 40 percent
- Progressive resistance training: loads bone mechanically and stimulates osteoblast activity; should include spinal loading and weight-bearing activities
- Impact exercise: running, jumping, and step-ups produce mechanical forces that stimulate bone formation in ways that swimming and cycling do not
- Adequate dietary calcium: 1200mg per day recommended for women over 50, achievable through dairy, fortified foods, and green leafy vegetables
- Vitamin D: required for intestinal calcium absorption; most adults in the UK are deficient in winter months
- Vitamin K2: directs calcium into bone rather than arterial walls; found in fermented foods and some cheeses
Sources
- Riggs, B.L., et al. (2002). Sex steroids and the construction and conservation of the adult skeleton. Endocrine Reviews, 23(3), 279-302.
- Kanis, J.A., et al. (2008). FRAX and the assessment of fracture probability in men and women from the UK. Osteoporosis International, 19(4), 385-397.
- Boonen, S., et al. (2004). Musculoskeletal effects of the menopause. Journal of Musculoskeletal and Neuronal Interactions, 4(4), 416-422.